Cerium based abrasive material, method of quality examination thereof, and method of production thereof

ABSTRACT

The present invention provides a method of examining quality of cerium-based abrasives which can simply determine their grinding characteristics. Specifically, the method employs X-ray diffractometry to examine qualities based on, for example, B/A wherein A and B are peak intensities relevant to Ln x O y  and LnF 3 , respectively. The present invention further provides: a method of producing a cerium-based abrasive which can give cerium-based abrasive with specific grinding characteristics; and a cerium-based abrasive which has specific grinding characteristics for specific purposes.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a national stage filing under 35 U.S.C. §371of PCT/JP01/08087 filed on 18 Sep. 2001, and designating the U.S.

TECHNICAL FIELD

This invention relates to a method of examining quality of cerium-basedabrasives, a method of producing a cerium-based abrasive, and acerium-based abrasive.

BACKGROUND ART

Recently, glass materials have been used for various purposes. Of these,advanced glass materials including glass substrates for optical andmagnetic disks, active matrix type liquid crystal displays (LCDs), colorfilters for liquid crystal TV sets, watches, calculators, LCDs forcameras, displays for solar cells or the like, LSI photomasks andoptical lenses, and optical lenses themselves are required to besurface-ground highly precisely.

These glass substrates are normally surface-ground using a cerium-basedabrasive composed of an oxide of rare-earth, in particular cerium oxide,as a main ingredient, because cerium oxide shows several times highergrinding efficiency than zirconium oxide and silicon dioxide forgrinding glass materials.

The common stock materials for cerium-based abrasives include rare-earthmaterials, e.g., carbonates, hydroxides and oxalates of rare-earthelements, and oxides produced by burning them. These stock materials arenormally prepared from bastnasite concentrate or other cerium-containingrare-earth materials by removing a part of rare-earth elements, e.g.,neodymium (Nd) and prasceodymium (Pr), and radioactive materials and thelike by a known chemical treatment.

A cerium-based abrasive from a carbonate or oxide of rare-earth isproduced by the following process. The process starts with slurrying orwet-crushing the stock material followed by chemical treatment with amineral acid and, as required, with hydrofluoric acid or ammoniumfluoride. The resultant slurry is subjected to filtration, drying androasting. Finally, it is crushed and classified to have an abrasive ofspecific particle size.

A cerium-based abrasive is required to have specific grindingcharacteristics for specific purposes. It is therefore necessary tograsp the grinding characteristics of a produced abrasive by, e.g.,analyzing these characteristics. For example, it is known that grindingspeed, referred to as grindability as one of important grindingcharacteristics, increases as the abrasive crystal size grows by theroasting step. It is however difficult to accurately grasp the grindingcharacteristics only from average particle size determined by the commonmethod of analyzing particle size distributions. Therefore, an abrasiveis examined, as required, for its quality by a test in which a testpiece is actually ground by the abrasive. The grinding test istime-consuming, because the ground test piece is weighed to determinegrindability, or ground surface is observed to confirm scratches.Therefore, a more simple method of examining the quality has been indemand. At the same time, a method of producing abrasives with specificgrinding characteristics can greatly save works for, e.g., qualityexamination, and hence is desirable, because it produces abrasives moreefficiently.

The present invention is developed in the light of the above problems.It is an object of the present invention to provide a method ofexamining quality of cerium-based abrasives which can simply determinetheir grinding characteristics. It is another object of the presentinvention to provide a method of producing a cerium-based abrasive whichcan give cerium-based abrasives with specific grinding characteristics.It is still another object of the present invention to provide acerium-based abrasive which has specific grinding characteristics forspecific purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the relationship between grindability and C/A ratio.

FIG. 2 shows the X-ray diffraction analysis data of Abrasive 1.

FIG. 3 shows the X-ray diffraction analysis data of Abrasive 6.

DISCLOSURE OF THE INVENTION

The inventors of the present invention have noted incorporation offluorine (F) in a cerium-based abrasive in order to solve the aboveproblems. Fluorine, which has been incorporated mainly to improvegrindability, forms a material of specific crystalline structure,depending on its content and roasting temperature, in abrasive or stocktherefore in which it is incorporated. More concretely, afluorine-containing compound is found to have the following crystallinestructure observed by X-ray diffractometry (XRD) in a cerium-basedabrasive or stock therefor in which it is incorporated:

(1) A fluorine (F)-containing compound is present in the form of LnF₃(e.g., LaF₃, wherein Ln is lanthanoids and La is lanthanum) in anF-containing oxide of cerium-based rare earth, and LnCO₃F in anF-containing carbonate of cerium-based rare earth in stock materialbefore roasting.

(2) When LnCO₃F-containing stock material is roasted, Ln having a largerionic radius decreases in content in a solid solution, being dischargedin the form of LnF₃ and contracting the Ln_(x)O_(y) lattice. Thischanges the crystal phase. For example, the crystal phase is transformedfrom the one identified as Ce_(0.5)Nd_(0.5)O_(1.75) by X-raydiffractometry (XRD) to the one identified asCe_(0.75)Nd_(0.25)O_(1.875). It should be noted, however, that thecrystal phase identified as Ce_(0.5)Nd_(0.5)O_(1.75) orCe_(0.75)Nd_(0.25)O_(1.875) has the main peak in the XRD pattern, evenat a low Nd content, from which it is considered to be an oxidecontaining La, which is normally present in a cerium-based abrasive atseveral tens % by atom on Ce, namely on the order of 0.2 to 0.7 timesthe Ce content in the number of atoms.

(3) LnF₃, when discharged at a high roasting temperature, grows as theLnOF phase (e.g., discharged LaF₃ grows as LaOF phase). Growth of thisphase will be retarded as a fluorine content increases, unless aroasting temperature is increased. Conversely, it grows at a lowerroasting temperature, as an F content decreases.

Ln (lanthanoids) in this specification contains at least one element ofLa (lanthanum), Ce (cerium) or Nd (neodymium) and LnF₃ is LaF₃, CeF₃ orthe like, and LnOF is LaOF, CeOF or the like. Ln_(x)O_(y) is La₂O₃,CeO₂, Ce_(0.5)Nd_(0.5)O_(1.75), Ce_(0.75)Nd_(0.25)O_(1.875) or the like,where normally the relationship 3/2≦y/x≦2 holds. These compoundsgenerally contain La at 5.0% to 85% per 100% of Ce, namely on the orderof 0.05 to 0.85 times the Ce content in the number of atoms, and Nd at1.0% to 50% per 100% of Ce, namely on the order of 0.01 to 0.5 times theCe content in the number of atoms.

The inventors of the present invention have further studied extensivelybased on the above XRD analysis results and found that whether or not acerium-based abrasive containing F and, at the same time, La or Nd tosome extent has good quality (grinding characteristics) can bedetermined by its XRD analysis results, reaching the present invention.

More concretely, the present invention provides a method of examiningquality (grinding characteristics) of a F-containing cerium-basedabrasive containing La or Nd each at 0.5% or more per 100% of Ce, all byatom, and having a specific surface area of 12 m²/g or less, the methodbeing based on XRD analysis with Cu—Kα₁ line as an X-ray source, whereinthe XRD analysis measures intensity A of the maximum peak “a” in adiffraction angle (2θ) range from 5 to 80°, and at least one ofintensity B of the maximum peak having a diffraction angle in a range of27.5±0.3° and smaller than the angle of the peak “a,” intensity C of themaximum peak having a diffraction angle in a range of 26.5±0.5°, andintensity D of the maximum peak having a diffraction angle in a range of24.2±0.5°, and at least one of the B/A, C/A and D/A ratios isdetermined, to examine the abrasive by comparing one of the ratios withthat of an abrasive of known grinding characteristics determined by XRDanalysis.

When an abrasive from a stock material containing limited quantities ofimpurities other than rare-earth elements, e.g., carbonate or oxide ofrare-earth, is analyzed by XRD, the maximum peak “a” (diffraction angle:2θ_(A), intensity: A) in a diffraction angle (2θ) range from 5 to 80° isnormally relevant to the [111] plane of Ln_(x)O_(y) (1≦y/x≦2). Themaximum peak “b” (diffraction angle: 2θ_(B), intensity: B) having adiffraction angle in a range of 27.5±0.3° and smaller than the angle ofthe peak “a,” if appears, indicates the presence of LnF₃. The maximumpeak “c” (diffraction angle: 2θ_(C), intensity: C) appearing atdiffraction angle in a range of 26.5±0.5° indicates the presence ofLnOF, and the maximum peak “d” (diffraction angle: 2θ_(D), intensity: D)appearing at a diffraction angle in a range of 24.2±0.5°, if appears,indicates the presence of LnF₃ as well as peak b.

It is found that there is a certain relationship between the XRDanalysis results (e.g., intensity A of the maximum peak relevant toLn_(x)O_(y), and B/A and D/A ratios, wherein B and D are intensities ofthe maximum peaks relevant to LnF₃) and quality (i.e., grindingcharacteristics related to scratches and grindability) of a cerium-basedabrasive. When a relationship between B/A, C/A or D/A ratio and grindingcharacteristics of a cerium-based abrasive of known grindingcharacteristics is established, grinding characteristics of anothercerium-based abrasive can be simply examined by measuring its XRDcharacteristics, e.g., B/A ratio. It is found by investigating theresults that the above examination method is particularly effective foran F-containing cerium-based abrasive containing La or Nd each at 0.5%or more per 100% of Ce, all by atom, and having a specific surface areaof 12 m²/g or less. In particular, the abrasive preferably containsfluorine at 1.0 to 15% by weight. At less than 1.0% by weight, theabrasive may deviate from the range in which it can be adequatelyexamined by the present invention; for example, it may not have the B/Aratio of 0.06 or more even when it produces a lot of scratches. At morethan 15% by weight, on the other hand, the abrasives satisfying theexamination standard of, e.g., B/A<0.06, will be rarely produced.

In the actual quality examination, a cerium-based abrasive is analyzedby XDR to measure the peak “a” and at least one of the peaks “b,” “c”and “d,” and find at least one of B/A, C/A and D/A ratios, and thecharacteristics of a cerium-based abrasive (grinding characteristics)are examined based on the established relationship between the grindingcharacteristics and the ratio.

The quality examination standards include whether the relationshipsB/A<0.06 or D/A<0.04 or not. It is found that an abrasive leaves only alimited number of scratches on the ground surface, e.g., glass surface,as its B/A or D/A ratio decreases, and that a cerium-based abrasivesatisfying the relationship B/A<0.06 or D/A<0.04 produces scratches toonly a limited extent and is practical. Basically, either the peak “b”or “d” may be used, but the peak “b” is more preferable because of itshigher peak intensity. However, when the peak “a” is identified as thatrelevant to Ce_(0.5)Nd_(0.5)O_(1.75) the diffraction angles of the peaks“a” and “b” are very close to each other, and peak intensity B isdifficult to determine when intensity B of the peak “b” is much lowerthan the maximum peak intensity A. In such a case, use of the peak “d”is more preferable.

Because it is found that an abrasive tends to have higher grindabilityas its C/A ratio increases, the ratio can be used to predictgrindability of an adhesive. It can be also used to examine quality ofan adhesive by knowing whether it attains or exceeds a standardcorresponding to a required grindability. This method allows to simplyexamine quality of cerium-based adhesives, thereby improving examinationwork efficiency, which, in turn, allows to conduct quality examinationsmore frequently, and to improve reliability of cerium-based abrasiveproducts.

When an abrasive is required to have certain quality (i.e., grindingcharacteristics) for a specific purpose, its quality is examined basedon the standard corresponding to the required grinding characteristics.More concretely, for example, consider a case where a cerium-basedabrasive is required to leave only a limited number of scratches on theground surface and its grindability can be low to some extent. In thiscase, B/A or D/A ratio may be used as the standard. In other words,those cerium-based abrasives of B/A≧0.06 or D/A≧0.04 should be rejected.The abrasive preferably satisfies B/A≦0.05, more preferably B/A≦0.03,still more preferably B/A≦0.01 to reduce scratches left on the groundsurface, or D/A≦0.03, more preferably D/A≦0.008 for the same reason. Theabrasive can be examined for its grindability based on only C/A ratio,when its grindability is sufficiently low, because such an abrasivenormally leaves few scratches on the ground surface and examination ofthe scratch-related characteristics based on B/A ratio may not benecessary. On the other hand, consider a case where an abrasive isrequired to leave only a limited number of scratches on the groundsurface and, at the same time, to have at least a given grindability. Inthis case, two ratios, B/A or D/A and C/A, are used as the standards. Inother words, a cerium-based abrasive passes the examination, when itsatisfies B/A<0.06 or D/A<0.04 and C/A corresponding to a requiredgrindability.

For an abrasive from a stock material, e.g., bastnasite concentrate,which contains a relatively large amount of impurities other thanrare-earth elements, the peak relevant to Ln_(x)O_(y) is the maximumpeak similarly to the other cases, but, when intensity of the peakrelevant to LnF₃ or LnOF is low, another material may have the maximumpeak in the above-described angle range. Nevertheless, however, it ispossible even in such a case to examine the abrasive quality based onthe B/A, C/A or D/A standards determined by the maximum peak in each ofthe above angle ranges, because the peak intensity relevant to anothermaterial is much lower than the maximum peak intensity A relevant toLn_(x)O_(y), or only slightly higher than the peak intensity B, c or Drelevant to LnF₃ or LnOF.

It is also possible to examine the abrasive quality in a similar manner,when the maximum peak “a” chosen for the present invention is replacedby another peak relevant to Ln_(x)O_(y), and/or the peak “c” chosen forthe present invention is replaced by another peak relevant to LnOF.Nevertheless, however, use of the maximum peaks “a” and “c” chosen forthe present invention is more preferable viewed from accuracy of theexamination, because each of them is the peak of the highest intensityfor each material. It should be also noted that peaks relevant to LnOFother than the peak “c” may not be distinguished from noise and lead toan erroneous conclusion, when its intensity is sufficiently low. It istherefore more preferable to use the peak “c” chosen for the presentinvention, also in consideration of the above.

The XRD peak intensity is defined as the top intensity for each peaksubtracted by the intensity commonly referred to as the back ground orbase line. The peak is also defined as the one whose intensity is 0.5%or more of the peak intensity A, and regarded as noise when itsintensity is lower than the above. It is therefore necessary to selectthe conditions for measuring an XRD peak under which it can be clearlydistinguished from noise, when its peak is 0.5% or more of the peakintensity A. Examples of these conditions are described in EXAMPLESdescribed later, although the adequate conditions are not limitedthereto.

The targets for XRD analysis include copper (Cu), to begin with,molybdenum (Mo), iron (Fe), cobalt (Co), tungsten (W) and silver (Ag),of which the Cu target is preferable in that it gives the highest peakintensity and hence more accurate results.

It would be better understood from the above description that acerium-based abrasive can be regarded as a good abrasive when itsatisfies the relationship B/A<0.06 or D/A<0.04, because such anabrasive will leave only a limited number of scratches on the groundsurface. An abrasive preferably satisfies B/A≦0.05, more preferablyB/A≦0.03, still more preferably B/A≦0.01 to reduce scratches left on theground surface, or D/A≦0.03, more preferably D/A≦0.008 for the samereason. A cerium-based abrasive can be regarded as an excellent abrasivewhen it satisfies the relationship 0.05≦C/A≦0.60, because it controlsformation of orange peel and has a sufficiently high grindability. Anabrasive having a C/A ratio less than 0.05, when used for grinding asurface, tends to produce orange peel, which will adversely affect thegrinding. On the other hand, an abrasive having a C/A ratio more than0.60 will have decreased grinding force, because of an insufficientcontent of Ln_(x)O_(y).

A cerium-based abrasive having required grinding characteristics for aspecific purpose can be provided by selecting adequate B/A or D/A andC/A ratios. For example, a cerium-based abrasive simultaneouslysatisfying the relationships B/A<0.06 or D/A<0.04 and 0.05≦C/A≦0.60 canbe provided as the one having a required practical grindability, becauseit leaves few scratches on the ground surface. A cerium-based abrasivesimultaneously satisfying the relationships B/A<0.06 or D/A<0.04 and0.10≦C/A≦0.60 is suitable for primary grinding of glass for liquidcrystal and hard disks. A cerium-based abrasive simultaneouslysatisfying the relationships B/A≦0.01 or D/A≦0.008 and 0.10≦C/A≦0.60 issuitable for finish grinding of glass for liquid crystal. A cerium-basedabrasive simultaneously satisfying the relationships B/A≦0.01 orD/A≦0.008 and 0.05≦C/A≦0.10 is suitable for finish grinding of harddisks.

The cerium-based abrasive of the present invention is normally used inthe form of slurry, after being dispersed in a dispersion medium, e.g.,water, to 5 to 30% by weight. The dispersion media useful for thepresent invention include water-soluble organic solvents, e.g., alcohol,polyhydric alcohol, acetone and tetrahydrofuran. However, water is anormal selection.

The cerium-based abrasive of the present invention preferably contains ahigh-molecular-weight organic dispersant. The organic dispersants usefulfor the present invention include polyacrylates, e.g., sodiumpolyacrylate, and carboxymethyl cellulose, polyethylene oxide andpolyvinyl alcohol. Such an organic dispersant works to prevent foamingduring the grinding process. It is incorporated in the abrasive at 0.1to 0.8% by weight, beyond which it will exhibit little further effect.

The inventors of the present invention have also studied a method ofproducing an abrasive having required grinding characteristics for aspecific purpose, based on the above-described XRD analysis results, tofind that at least one of the B/A, C/A and D/A ratios, determined by XRDpeak intensities, changes regularly with a fluorine content of theabrasive or temperature at which it is roasted, reaching the inventiondescribed below.

This inventions relates to a method of producing a fluorine-containingcerium-based abrasive containing La or Nd each at 0.5% or more per 100%of Ce, all by atom, and having a specific surface area of 12 m²/g orless, involving fluorination treatment of the abrasive before it isroasted, wherein a fluorine content and roasting temperature aredetermined by the XRD analysis results. More concretely, thecerium-based abrasive is analyzed by XRD with Cu—Kα₁ line as an X-raysource, to determine the maximum peak intensities A, B, C and D in adiffraction angle (2θ) range from 5 to 80°, 27.5±0.3° smaller thandiffraction angle of peak a, 26.5±0.5° and 24.2±0.5°, respectively, andat least one of B/A, C/A and D/A ratios is compared with that of anabrasive of known production conditions, determined by XRD analysis, todetermine the fluorine content and roasting temperature.

It is found, as described earlier, a cerium-based abrasive having lowerB/A and D/A ratios leaves less scratches on the ground surface.Therefore, the production conditions for an abrasive of requiredgrinding characteristics, e.g., fluorine content and roastingtemperature, can be simply determined, by determining in advance therelationship for an abrasive of known production conditions (e.g.,fluorine content and roasting temperature) between XRD-determined B/A orD/A ratio and these conditions and comparing these ratios of theabrasives with each other. A cerium-based abrasive can be produced underthe fluorine content and roasting temperature thus simply determined.For example, a cerium-based abrasive will leave few scratches on theground surface, when fluorine content and roasting temperature arecontrolled for the abrasive in such a way that it satisfies therelationship B/A<0.06. The abrasive preferably satisfies B/A≦0.05, morepreferably B/A≦0.03, still more preferably B/A≦0.01 to reduce scratchesleft on the ground surface. For D/A ratio, the production conditions arecontrolled to give the relationship D/A<0.04, preferably D/A≦0.03, morepreferably D/A≦0.008 for the same reason.

For C/A ratio, on the other hand, it is found that there is an adequaterange, below which orange peel tends to occur to adversely affect thegrinding, and above which grinding force tends to decline, both beingundesirable. Therefore, the production conditions for an abrasive withrequired grinding characteristics, e.g., fluorine content and roastingtemperature, can be simply determined, by determining in advance therelationship for an abrasive of known production conditions (e.g.,fluorine content and roasting temperature) between the XRD-determinedC/A ratio and these conditions and comparing the ratio of the abrasiveswith each other. A cerium-based abrasive can be produced under thefluorine content and roasting temperature simply determined. Acerium-based abrasive will be an excellent abrasive, and hencedesirable, when it satisfies the relationship 0.05≦C/A≦0.60, because itcontrols formation of orange peel and has a sufficiently highgrindability.

Controlling a fluorine content of the abrasive and roasting temperaturebased on the two values of B/A or D/A and C/A ratios can give acerium-based abrasive which leaves few scratches on the ground surfaceand has a required grindability or higher. More concretely, a fluorinecontent and roasting temperature are controlled to produce acerium-based abrasive in such a way that the abrasive has a B/A ratio ofless than 0.06 and, at the same time, C/A ratio which gives a requiredgrindability.

The method of the present invention produces a cerium-based abrasiveunder the conditions of fluorine content and roasting temperature,controlled to give the abrasive having the required XRD-determinedintensity ratios, e.g., B/A ratio. The XRD analysis to determine theintensity ratios such as B/A is used for the quality examination, asdescribed earlier. The quality examination is carried out routinely. Itis advantageous when the quality examination results can be used forsetting or adjusting the production conditions, because the additionalgrinding test or the like is no longer necessary. As described above,the XRD-aided quality examination is much more simple than the grindingtest. The method of the present invention for producing a cerium-basedabrasive involves XRD analysis (quality examination) conducted for theabrasive as soon as it is produced, and the fluorine content androasting temperature predicted by the intensity ratios, e.g., B/A, areimmediately fed back for the next abrasive products. The presentinvention, therefore can produce a high-quality, stable cerium-basedabrasive more efficiently.

One example of the method of producing a cerium-based abrasive isdescribed in detail.

The stock materials for a cerium-based abrasive include oxide of rareearth, carbonate of rare earth and bastnasite concentrate. The oxide ofrare earth is obtained as the mixed oxides of rare earth elements byroasting the stock in the form of, e.g., carbonates, hydroxides andoxalates. Bastnasite concentrate is powdered ore having fluorinatedcarbonate of rare earth as its major component, obtained throughtreatments such as crushing, flotation, acid leaching, drying.

The stock materials for cerium-based abrasive is crushed to givenparticle size to use. The stock material is crushed by, e.g., a ballmill in the presence of a solvent, to an average particle size of around0.5 to 3 μm.

The crushed stock, when it is bastnasite concentrate, is normallytreated with a mineral acid, e.g., hydrochloric, sulfuric or nitricacid, adjusted at a concentration of around 0.1 to 2N. This treatmentreduces contents of, e.g., alkali metals (e.g., Na and Ca) andalkali-earth metals, and controls abnormal grain growth in thesubsequent roasting step.

When an oxide or carbonate of rare earth is used as the stock, on theother hand, it is normally slurried and fluorination-treated with afluorine-containing compound, e.g., ammonium fluoride or hydrofluoricacid, or an aqueous solution thereof. The fluorine content is preferably5 to 100 g/L.

Even when bastnasite concentrate is used as the stock material, it maybe fluorination-treated to increase its fluorine content. Moreover, evenwhen an oxide or carbonate of rare earth is used as the stock material,it may be treated with a mineral acid, depending on its alkali andalkali-earth metal contents.

The cerium-containing stock material of rare earth, after being treatedwith a mineral acid or fluorination-treated, is dried and then roastedin an electrical furnace or the like at 600 to 1100° C., preferably 700to 1000° C., for around 1 to 10 hours. It is then left for cooling,crushed and classified to obtain an abrasive. The abrasive preferablyhas an average particle size of around 0.05 to 3.0 μm and containsfluorine at 1 to 15% by weight, preferably 1 to 10%. It is possible tocontrol particle size of the abrasive by controlling its fluorinecontent and roasting temperature.

A fluorine content of a cerium-based abrasive and temperature at whichit is roasted can be predicted by a specific surface area and the XRDanalysis with Cu—Kα₁ line as the X-ray source, wherein the XRD analysismeasures intensity A of the maximum peak “a” in a diffraction angle (2θ)range from 5 to 80°, and at least one of intensity B of the maximum peakhaving a diffraction angle in a range of 27.5±0.3° and smaller than theangle of the peak “a,” intensity C of the maximum peak having adiffraction angle in a range of 26.5±0.5° and intensity D of the maximumpeak having a diffraction angle in a range of 24.2±0.5°, and at leastone of the B/A, C/A and D/A ratios is used to control fluorine contentand roasting temperature.

The abrasive preferably has a specific surface area of 12 m²/g or less,more preferably 10 m²/g or less, still more preferably 8 m²/g or less.The abrasive having a specific surface area of more than 12 m²/g may nothave a required particle size to increase grindability, even when theparticles grow during the roasting step, leaving practical problems. Thespecific surface area is determined by the common BET method withnitrogen gas.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described more concretely by EXAMPLES.

The stock materials used in EXAMPLES were an oxide of rare earth havinga total rare earth oxide (TREO) content of 99%, and CeO₂ and La₂O₃ at 57to 61% and 31 to 34%, respectively based on the TREO; and bastnasiteconcentrate having a TREO content of 67 to 73%, and CeO₂ and La₂O₃ at 40to 43% and 24 to 26%, respectively based on the TREO, all by weight.Each was ball-milled in the presence of a solvent (water) to have apowder of 1.0 μm in average particle size. It was treated with a mineralacid (1N hydrochloric acid) in the case of bastnasite concentrate, andwith an aqueous solution of ammonium fluoride containing fluorine at 15to 25 g/L in the case of oxide of rare earth to have a given fluorinecontent. The resultant slurries were filtered, dried and roasted in anelectrical furnace at a given roasting temperature (refer to Table 1)for 2 hours, and then left for cooling, crushed and classified to obtainAbrasives 1 to 10 (shown in Table 1). Abrasives 1 to 6 and 10 were fromoxide of rare earth as the stock material, and Abrasives 7 to 9 frombastnasite concentrate. Table 1 gives roasting temperature and fluorinequality (fluorine content) of these abrasives. Fluorine was analyzed bythe fluorine ion electrode method, after the sample was molten in analkali and extraction with hot water.

Each of Abrasives 1 to 10 was tested to evaluate grindability andscratches left on the ground surface, where it was dispersed in water tohave a 10 wt % abrasive slurry and used to grind glass for a 65mm-diameter planar panel by a high-speed grinder at a grinding pressureof 1.54 MPa (15.7 kg/cm²). Evaluation of grindability and scratches wereevaluated on the surface of glass after grinding.

For evaluation of grindability, the sample of glass for a planar panelwas weighed before and after the grinding to determine weight loss, bywhich cut thickness was estimated.

Scratches were evaluated by transmission and reflection. Moreconcretely, the ground surface was irradiated with light from a halogenlamp (300,000 lux) to observe the glass surface, to evaluate thescratches by the extent (size and the numbers) thereof, scored bydeducting points from 100 points. The results are given in Table 1.

Each abrasive was measured for its specific surface area and degree ofcohesion. Specific surface area was measured for the accurately weighedsample by an automatic specific surface area analyzer (Manufactured byYuasa Ionics Co., Ltd., Multisorb 12). Degree of cohesion was measuredby a powder tester (Hosokawa Micron Co., Ltd.), for which 355, 250 and44 μm sieves were used. The results are given in Table 1.

With the use of X-ray diffractometer MXP18 (Manufactured by MAC ScienceCo., Ltd.), Abrasives 1 to 10 were analyzed by XRD to determine XRDintensity, with a Cu target and Cu—Kα₁ line as the X-ray source underthe conditions of tube voltage: 40 kV, tube current: 150 mA, diffractionangle (2θ) range: 5 to 80°, sampling width: 0.02°, and scanning rate:4°/minute. The results are given in Table 2. The XRD analysis data ofAbrasives 1 and 6 are given in FIGS. 2 and 3.

The XRD analysis measured intensity A of the maximum peak “a” and itsdiffraction angle θ_(A) in a diffraction angle (2θ) range from 5 to 80°,diffraction angle θ_(B) and intensity B of the maximum peak having adiffraction angle in a range of 27.5±0.3° and smaller than the angle ofthe peak “a,” diffraction angle θ_(C) and intensity C of the maximumpeak having a diffraction angle in a range of 26.5±0.5°, and diffractionangle θ_(D) and intensity D of the maximum peak having a diffractionangle in a range of 24.2±0.5°. The results are given in Table 2, wherepeak intensities B, C and D are relative to that of peak intensity A(100). As described earlier, the peak is defined as the one whoseintensity is 0.5% or more of the peak intensity A, and the peakintensities B, C and D are regarded as zero when they are lower than0.5% of the peak intensity A.

The relationship between grindability and C/A ratio is shown in FIG. 1.

TABLE 1 Contents (Ce = 100 parts by atom) Roasting Degree La NdEvalutions of temper- Fluorine Specific of Parts Parts Grind- scratchesature content Surface Cohesion by by ability Trans- [° C.] [%] [m²/g][%] atom atom [μm] mission Reflection Abrasive 1 810 4.2 7.84 49.1 54.62.2 25.0 100 100 Abrasive 2 810 4.7 7.37 40.6 59.7 7.9 24.0 100 100Abrasive 3 920 5.2 3.75 59.4 59.7 1.8 35.7 100 97 Abrasive 4 970 5.03.24 66.1 61.5 4.5 34.6 100 97 Abrasive 5 980 7.3 2.29 85.8 55.1 2.840.4 100 76 Abrasive 6 990 7.8 1.82 88.9 57.8 3.5 39.5 80 All glass testpieces have many scratches Abrasive 7 770 5.8 8.45 25.5 25.2 7.6 25.3100 100 Abrasive 8 800 5.6 7.64 35.6 25.2 8.2 25.5 100 100 Abrasive 9970 7.1 1.60 23.5 25.3 7.3 38.0 100 100 Abrasive 10 550 4.3 15.76 74.558.2 3.3 7.5 100 100

TABLE 2 XRD intensity and intensity ratio C A B D C/A B/A D/A Abrasive 18 100 0 0 0.08 0.00 0.00 Abrasive 2 7 100 0 0 0.07 0.00 0.00 Abrasive 350 100 0 0 0.50 0.00 0.00 Abrasive 4 47 100 0 0 0.47 0.00 0.00 Abrasive5 36 100 6 4 0.36 0.06 0.04 Abrasive 6 34 100 17 10 0.34 0.17 0.10Abrasive 7 8 100 0 0 0.08 0.00 0.00 Abrasive 8 10 100 0 0 0.10 0.00 0.00Abrasive 9 53 100 0 0 0.53 0.00 0.00 Abrasive 10 3 100 0 0 0.03 0.000.00

As shown in Table 1, Abrasive 10, having a specific surface areaexceeding 12 m²/g, is a poor abrasive, because of its insufficientproperties of very low grindability and high adhesion to the surface tobe ground, although good in grinding evaluation.

Abrasives 1 to 9, having a specific surface area of 12 m²/g or less,have a correlation between the C/A ratio and grindability, as shown inTables 1 and 2 and FIG. 1. In other words, grindability tends toincrease as the C/A ratio increases, and grindability can be estimatedfor grinding from the C/A ratio.

It is found, as shown in Tables 1 and 2, that Abrasives 1 to 4 and 7 to9 out of Abrasives 1 to 9 which have a specific surface area of 12 m²/gor less but 1.0 m²/g or more have zero peak intensities B and D, andhence zero B/A and D/A ratios, leaving few scratches on the groundsurface. On the other hand, scratches are produced rapidly in a B/A orD/A region of B/A≧0.06 or D/A≧0.04 (Abrasives 5 and 6). This conceivablyresults from increased fluorine content to further grow the LnOF phase(e.g., LaOF phase), which, although increasing grindability, leaves theLnF₃ phase (e.g., LaF₃ phase) because of the limited growth of the LnOFphase (e.g., LaOF phase) at the normal roasting temperature (around 600to 1100° C.). Abrasives 5 and 6 have higher B/A and D/A ratios butslightly lower C/A ratio than Abrasives 3 and 4.

It is therefore judged that a cerium-based abrasive leaves lessscratches on the ground surface as its B/A or D/A ratio decreases, and,conversely, leaves more scratches when its B/A or D/A is in a region ofB/A≧0.06 or D/A≧0.04. Grindability of an abrasive can be judged based ona C/A ratio.

A cerium-based abrasive leaving only a limited number of scratches onthe ground surface can be produced by adjusting its fluorine content andtemperature at which it is roasted, based on the B/A or D/A ratio. Itwill leave few scratches, when its fluorine content and temperature atwhich it is roasted are adjusted in such a way to avoid B/A≧0.06 orD/A≧0.04.

Moreover, a cerium-based abrasive having a given grindability or morecan be produced when its fluorine content and temperature at which it isroasted are adjusted based on the C/A ratio.

Therefore, a cerium-based abrasive leaving few scratches on the groundsurface and having a given grindability or more can be produced, whenits fluorine content and temperature at which it is roasted are adjustedbased on B/A or D/A and C/A ratios. More concretely, it is recommendedto adjust fluorine content and roasting temperature in such a way toavoid B/A≧0.06 or D/A≧0.04, and, at the same time, to keep a C/A ratiocorresponding to a required grindability.

A cerium-based abrasive can guarantee that it leaves few scratches onthe ground surface, when it satisfies B/A<0.06 or D/A<0.04. The abrasivepreferably satisfies B/A≦0.05, more preferably B/A≦0.03, still morepreferably B/A≦0.01 to reduce scratches left on the ground surface, orD/A≦0.03, more preferably D/A≦0.008 for the same reason.

A cerium-based abrasive can be sufficiently serviceable, when itsimultaneously satisfies the relationships B/A<0.06 or D/A<0.04 and0.05≦C/A≦0.60, because it leaves few scratches on the ground surface andsecures a grindability of around 23 to 40 μm or more as shown in Tables1, 2 and FIG. 1. A cerium-based abrasive simultaneously satisfying therelationships B/A<0.06 or D/A<0.04 and 0.10≦C/A≦0.60 is suitable forprimary grinding of glass for liquid crystal and hard disks, because itleaves few scratches on the ground surface and secures a grindability ofaround 23 to 40 μm or more. A cerium-based abrasive simultaneouslysatisfying the relationships B/A≦0.01 or D/A≦0.008 and 0.10≦C/A≦0.60 issuitable for finish grinding of glass for liquid crystal, because itleaves essentially no scratches on the ground surface and secures agrindability of around 25 to 40 μm or more. A cerium-based abrasivesimultaneously satisfying the relationships B/A≦0.01 or D/A≦0.008 and0.05≦C/A≦0.10 is suitable for finish grinding of hard disks, because itleaves essentially no scratches on the ground surface and secures agrindability of around 23 to 25 μm or more.

INDUSTRIAL APPLICABILITY

The present invention is for examination of quality (grindingcharacteristics) of a cerium-based abrasive. The method of the presentinvention for examining quality of cerium-based abrasives allows theabrasive quality to be simply examined, and screen the cerium-basedabrasives of required grinding characteristics. The cerium-basedabrasive of the present invention has grinding characteristics forspecific purposes, and can be suitably used for primary grinding ofglass for liquid crystal and hard disks, finish grinding of glass forliquid crystal, or finish grinding of hard disks. The method of thepresent invention can produce a cerium-based abrasive which has grindingcharacteristics for specific purposes.

What is claimed is:
 1. A method for examining the quality of a ceriumabrasive having a specific surface area of no more than 12 m²/g andcontaining fluorine and at least 0.5 atomic parts La or Nd per 100atomic parts Ce, comprising the steps of: (a) performing an X-raydiffraction (XRD) analysis on the cerium abrasive with Cu—Kα₁ line as anX-ray source, and measuring intensity A and at least one of intensitiesB, C and D, wherein intensity A is the maximum peak “a” in a diffractionangle (2^(θ)) range from 5 to 80°, intensity B is the maximum peakhaving a diffraction angle in a range of 27.5±0.30°, and less than theangle of peak “a”, intensity C is the maximum peak having a diffractionangle in a range of 26.5±0.5°, and intensity D is the maximum peakhaving a diffraction angle in a range of 24.2±0.5°; and (b) evaluatingthe quality of the abrasive by comparing at least one of the ratios B/A,C/A or D/A of the cerium abrasive with the corresponding B/A, C/A or D/Aratios, as determined by XRD analysis, of an abrasive of known grindingcharacteristics.
 2. A cerium abrasive having a specific surface area ofno more than 12 m²/g and containing fluorine and at least 0.5 atomicparts La or Nd per 100 atomic parts Ce, the cerium abrasive having anintensity ratio B/A of less than 0.06, wherein intensity A and intensityB are determined by XRD analysis with Cu—Kα₁ line as an X-ray source,and intensity A is the maximum peak “a” in a diffraction angle (2^(θ))range from 5 to 80° and intensity B is the maximum peak having adiffraction angle in a range of 27.5±0.3°, and less than the angle ofpeak “a.”
 3. A cerium abrasive having a specific surface area of no morethan 12 m²/g and containing fluorine and at least 0.5 atomic parts La orNd per 100 atomic parts Ce, the cerium abrasive having an intensityratio D/A of less than 0.04, wherein intensity A and intensity D aredetermined by XRD analysis with Cu—Kα₁ line as an X-ray source, andintensity A is the maximum peak “a” in a diffraction angle (2^(θ)) rangefrom 5 to 80° and intensity D is the maximum peak having a diffractionangle in a range of 24.2±0.5°.
 4. The cerium abrasive of claim 2, havingan intensity ratio C/A no less than 0.05 and no more than 0.60, whereinintensity C is determined by XRD analysis with Cu—Kα₁ line as an X-raysource and intensity C is the maximum peak having a diffraction angle ina range of 26.5±0.5°.
 5. The cerium abrasive of claim 3, having anintensity ratio C/A no less than 0.05 and no more than 0.60, whereinintensity C is determined by XRD analysis with Cu—Kα₁ line as an X-raysource and intensity C is the maximum peak having a diffraction angle ina range of 26.5±0.5°.
 6. The cerium abrasive of claim 4, having anintensity ratio C/A no less than 0.10.
 7. The cerium abrasive of claim2, having an intensity ratio B/A of no more than 0.01 and C/A no lessthan 0.10 and no more than 0.60, wherein intensity C is determined byXRD analysis with Cu—Kα₁ line as an X-ray source and intensity C is themaximum peak having a diffraction angle in a range of 26.5±0.5°.
 8. Thecerium abrasive of claim 2, having an intensity ratio B/A of no morethan 0.01 and C/A no less than 0.05 and no more than 0.10, whereinintensity C is determined by XRD analysis with Cu—Kα₁ line as an X-raysource and intensity C is the maximum peak having a diffraction angle ina range of 26.5±0.5°.
 9. The cerium abrasive of claim 3, having anintensity ratio CIA no less than 0.10 and no more than 0.60, whereinintensity C is determined by XRD analysis with Cu—Kα₁ line as an X-raysource and intensity C is the maximum peak having a diffraction angle ina range of 26.5±0.5°.
 10. The cerium abrasive of claim 9, having anintensity ratio D/A of no more than 0.008.
 11. The cerium abrasive ofclaim 3, having an intensity ratio D/A of no more than 0.008 and C/A noless than 0.05 and no more than 0.10, wherein intensity C is determinedby XRD analysis with Cu—Kα₁ line as an X-ray source and intensity C isthe maximum peak having a diffraction angle in a range of 26.5±0.5°. 12.A method for optimizing the fluorine content and roasting temperature ina process for producing a cerium abrasive having a specific surface areaof no more than 12 m²/g and containing fluorine and at least 0.5 atomicparts La or Nd per 100 atomic parts Ce, the process comprising the stepsof fluorinating and then roasting a cerium stock material, the methodcomprising determining the optimum fluorine content of the ceriumabrasive after the fluorinating step and the temperature for theroasting step by comparing at least one of intensity ratios B/A, C/A andD/A of the cerium abrasive with the corresponding B/A, C/A or D/Aratios, as determined by XRD analysis, of an abrasive produced at knownfluorine content and roasting temperatures, wherein intensities A, B, Cand D are determined by XRD analysis with Cu—Kα₁ line as an X-raysource, and intensity A is the maximum peak “a” in a diffraction angle(2^(θ)) range from 5 to 80°, intensity B is the maximum peak having adiffraction angle in a range of 27.5±0.3°, and less than the angle ofpeak “a,” intensity C is the maximum peak having a diffraction angle ina range of 26.5±0.5°, and intensity D is a maximum peak having adiffraction angle in a range of 24.2±0.5°.
 13. The method according toclaim 12, wherein the fluorine content in the fluorination step and thetemperature for the roasting step are adjusted so that the ceriumabrasive has a B/A ratio of less than 0.06 and a D/A ratio of less than0.04.